$color:#007fff;


.outline-btn {
  padding: 15px 30px;
  border-radius: 6px;
  font-size: 16px;
  color: $color;
  position: relative;
  background: transparent;
  overflow: hidden;
  border-color: transparent;
}

.outline-btn::before {
  content: "";
  position: absolute;
  width: 200%;
  height: 200%;
  z-index: -2;
  background-color: $color;
  left: 50%;
  top: 50%;
  animation: rotation 1s linear infinite;
  transform-origin: left top;
  overflow: hidden;
}

.outline-btn::after {
  content: "";
  position: absolute;
  background-color: #000;
  --s:2px;
  width: calc(100% - 2*var(--s));
  height: calc(100% - 2*var(--s));
  top: var(--s);
  left: var(--s);
  z-index: -1;
  border-radius: inherit;
}

@keyframes rotation {
  to {
    transform: rotate(1turn);
  }
}